A constant speed of light in all reference frames? Surely you can't be serious.
in [Relativity]
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From: Ste on 4 Mar 2010 02:13 On 3 Mar, 17:21, mpalenik <markpale...(a)gmail.com> wrote: > On Mar 3, 12:15 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > On Mar 3, 11:04 am, mpalenik <markpale...(a)gmail.com> wrote: > > > > On Mar 3, 11:21 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Mar 2, 8:12 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > > > > > > > It is not a function of finite propagation speeds, this we know, > > > > > > because we took into account the finite propagation speeds in our > > > > > > procedure for determining simultaneity/nonsimultaneity. Do you not > > > > > > remember that? > > > > > > I beg to differ. It is not a "mere" or "simple" function of finite > > > > > propagation speed, but it *is* a function of it IMO. RoS only took it > > > > > into account by allowing us to use different time coordinates in each > > > > > frame. If the speed of light was infinite there would be no RoS. > > > > > I disagree. All that is needed in relativity of simultaneity is a > > > > signal speed that can be VERIFIED to be the same from both events by > > > > either observer. Since the distance from the events to the observer is > > > > equal, as verifiable at any time by each observer, we learn from this > > > > that each observer KNOWS the propagation delays from each event to the > > > > observer are equal. This acknowledges the propagation delays > > > > completely, but simply allows for verification that they are the same. > > > > Then the determination of simultaneity or nonsimultaneity of the > > > > original events is completely unambiguous: If the observer receives > > > > both signals at the same time, then (because the propagation delays > > > > are the same) the original events were simultaneous; if the observer > > > > receives both signals at different times, then (because the > > > > propagation delays are the same) the original events were > > > > nonsimultaneous. > > > > Ste, there is a very easy thought experiment that I posted a few pages > > > back that proves this wrong. Get someone to run through it with you. > > > I don't have the patience or time. Even if a moving observer receives > > > two pulses at the same time while half way between the two sources, he > > > will conclude that they were not emitted at the same time BECAUSE the > > > speed of light is the same in every frame. If the speed of light were > > > different in the moving observer's frame (like it is with sound), you > > > would be correct. But since the speed of light is the same in the > > > moving observer's frame as in the rest frame, he has no choice but to > > > conclude that the two pulses were emitted at different times, despite > > > the fact that he receives them at the same time and he is half way > > > between the two emitters. > > > ??? > > I'll post it again: > > ------x----- > > ^ > > ------x----- > > An object, indicated by the "^" is moving vertically along the > screen. The two x's send out light pulses simultaneously in the rest > frame that both reach the moving ^ when it is exactly half way between > the two x's. > > Because of this, the ^ will recieve both pulses simultaneously in > every frame--however, in the ^ frame, the observer will say that the > two x's did not emmit the light pulse simultaneously, even though he > recieved both pulses simultaneously. > > This proves that SR has nothing to do with correcting for propagation > delays. I don't have the time or patience to explain this to Ste, but > I'm sure it's easily comprehensible to everyone else. > > (PD: note that since it's the x's moving in the ^ frame, and since the > light is emitted when the lower x is closer to the ^ and the upper x > is farther, the moving ^ must conclude that the light from the upper x > was emitted first, even though both pulses hit him at the same time. > This is because the light is moving at speed c in his frame and not c > +v and c-v. This probably isn't clear to Ste, but I think you see > what I'm going for) Mark, I'm unable to understand the basis your argument, even though I understand what you are saying. That is, you state your assertions baldly, and without any explanation. As far as I'm concerned, the receiver ^ in your example would disagree about simultaneity because there is no way to conduct a test at a single instant in time, and therefore over the course of the measurement process he will in fact have moved closer to one event while moving away from the other (and, for example, the asymmetry would be manifest in the Doppler shifting of both sources).
From: Peter Webb on 4 Mar 2010 02:36 In a book by Feynman I read an explaination how the difference in coordinate system had no effect on mechanics. I forget where it was at the moment but I do know it was a convincing argument. _____________________________________________ Yes, it is really important point; changing co-ordinate systems cannot change the results of physical experiments. It is important historically because it led the theory of Gauge theories, and was key to developing GR. That the choice of x, y and z axis cannot affect physical experiments is a statement that the Universe is isotropic; that you can choose the origin to be anywhere reflects the fact that physical laws are location independent. These give rise to natural symmetry groups in equations, which constrain the sorts of equations that can actually model physical processes. For example, if you wrote out F = ma = gmM/r^2 in terms of x, y and z co-ordinates, if x=a, y=b, x=c, t=t1 is a solution to some equation then so is x=b, y=a, z=c, t=t1 for the rotated experiment, as the choice of axis is arbitrary. This is not true of Maxwell, where (if I have got this right) switching two axis changes the sign of the time term, x=b, y=a, z=c, t=-t1. It was generalising this concept that led to GR; as I understand it (and I don't claim to understand GR well), this is almost but not quite enough to determine the equations of GR uniquely. This is all lovely, deep, profound stuff, but the practical reality is that to actually use it, you have know something about group theory, and Lie groups in particular. For the amateur physicist, this is well off in left field, group theory AFAIK is not taught in secondary school, at least that I recall.
From: Ste on 4 Mar 2010 03:12 On 3 Mar, 20:01, mpalenik <markpale...(a)gmail.com> wrote: > On Mar 3, 12:52 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > No. In SR, clocks *appear* to run slower as you are increasing your > > distance from the clock. The effect is entirely apparent in SR. > > You must just go through the entire thread and not pay any attention > to what anybody says. Ever. > > 1) What you've stated above is not an effect of SR. It is an effect > of propagation delay, which was used to calculate c from the motion of > the moons of jupiter hundreds of years ago. Ok. > 2) If you were to move TOWARD the clock, it would appear to run > faster. But SR says nothing about whether you are moving toward or > away from an object. <suspicious eyebrow raised> Ok. > 3) The amount that the clock would appear to slow down is DIFFERENT > from the amount that SR predicts the clock *actually* slows down Really? I'm growing increasingly suspicious. In what way does SR predict the "actual" slowdown, as opposed to the "apparent" slowdown? And for example, if we racked up the value of 'c' to near infinity, would SR still predict an "actual" slowdown, even though the propagation delays would approach zero? > 3) This does not explain why atomic clocks on a jet register different > times AFTER being brought to rest than do their counterparts which > have been at rest the entire time--or why the difference in time that > they register is exactly consistant with the predictions of > relativity. Indeed, because SR doesn't deal with acceleration. > I know this isn't the first time this has been told to you, although > maybe not all at once. Do you just not pay any attention at all to > what anybody tells you? I pay attention. It's just that I've been asking for weeks for an explanation for this assertion that time slows down in SR above and beyond the "apparent" effect due to propagation delays, and all I keep getting in return is a bald assertion that this is the case, even though I've made it quite clear that I do not find this bald assertion believable.
From: Ste on 4 Mar 2010 03:13 On 3 Mar, 22:23, "Inertial" <relativ...(a)rest.com> wrote: > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > news:64d02f70-01e4-44a5-a5ab-41429bf37f71(a)q15g2000yqj.googlegroups.com... > > > I'm sure I said something about the ludicrous assertions that some > > people here have made about the conceptual basis of SR. That is, > > assertions that verge on meaningless, like "rotation into time" as an > > explanation for length contraction. Or even observed time dilation (in > > SR) being "real" as opposed to merely a function of propagation > > delays. But none of this fundamentally challenges SR. > > Time dilation isn't anything to do with propagation delays .. they do NOT > cause time dilation. It IS real in that it has been measured > experimentally. > > Your denial of reality is another trademark of a crackpot. I'm not denying it. I'm saying experiments that involve acceleration are the realm of GR (as I understand it), and that acceleration is the cause of "real" time dilation. We're talking about SR, and therefore we cannot be talking about any experiment that involves acceleration.
From: Ste on 4 Mar 2010 03:28
On 3 Mar, 22:31, "Inertial" <relativ...(a)rest.com> wrote: > "Ste" <ste_ro...(a)hotmail.com> wrote in message > > >> and 80 foot ladders can fit through 40 feet barns, > > > It remains slightly unclear, but I'm inclined to say no, > > Then you do not understand or accept SR. > > > although it > > can certainly be made to appear to happen in certain circumstances. > > So if you close the doors simultaneously on a barn and the rod is inside you > think that means it is not REALLY inside? The question is of measuring simultaneity. I can accept that, from certain perspectives, the doors would appear to close simultaneously with the ladder inside, but that in fact the distant door opened before the nearest door even shut (and hence the ladder was never physically inside with both doors shut). This also explains why, from the ladders perspective, the barn can get apparently *even smaller*, and yet the ladder can still pass through. To conceive of length contraction being real, it would surely be detectable already, and moreover it would indicate a preferred frame of reference (because even from the ladder's frame, the ladder would have to shrink relative to the barn - which would manifest itself as the barn growing to apparently twice its real size). > >> If, on the other hand, you do not believe in the twin "paradox" actually > >> happening, you don't believe in SR. > > > We resolved the twins paradox months ago. The astronaut twin undergoes > > asymmetrical acceleration, and that is why he returns younger. > > >> If you do believe the predictions of SR > >> that one twin is older, then you believe that time dilation is more than > >> some mathematical fiction, its what actually happens in the real world.. > > > On the contrary. The involvement of acceleration, which is the domain > > of GR, makes me wonder why this is held to be a paradox in SR at all. > > SR handles acceleration just fine I doubt it. Otherwise you'd get a contradiction in the twins paradox. > > And yes, the acceleration causes real effects for the astronaut twin. > > >> So, when relativity predicts that one twin will age more than the other, > >> is > >> this just some mathematical truth, or is it what really happens as well? > > > It really happens, due to acceleration. > > >> So, do you believe that SR is correct in its prediction (for example) > >> that > >> if one twin were to be sent off into space at 0.9c for 10 years they > >> would > >> have aged less on their return than the twin that stayed at home? > > > I'm not sure SR does predict this. > > Of course it does .. that is the twins paradox you just said you understnood > !! > > > As I understand it, GR is required > > to predict this effect. > > Wrong > > > The problem for SR was, as I understand it, > > explaining why SR *doesn't* predict that effect. > > It DOES predict it. My god you are SO DAMNED IGNORANT of what you > ponficiate about. As far as I know, Einstein used GR to resolve the paradox, based on the fact that the astronaut twin undergoes "real" acceleration, whereas the Earth (and the homebody twin) does not. > >> Do you agree its correct when it says that an 80 foot ladder could fit > >> inside a 40 foot barn? > > > No, I'm not confident about that prediction. I think it's more likely > > to be an apparent effect. > > What is only 'apparent' about shutting the doors on a barn simultaneously > with a long rod fully ensloed between them? Do you think it is all done > with mirrors? It doesn't need to be done with mirrors. A person standing at one door of the barn who observes the doors close simultaneously, would not observe simultaneity when standing at the other door (when standing at the other door, he would observe that other door to shut long before the first door). Hence by careful timing of the doors, and crafty position of the observer, it can be made to appear that the doors shut simultaneously while, in fact, they did not. And just to be clear, my concept of "simultaneity" is that which would be simultaneous if information propagated instantaneously. |